1. Field of the Invention
The present invention relates to a fluid compressor, more specifically to a type for compressing a refrigerant gas in a refrigerating cycle.
2. Description of the Related Art
USP Nos. 4,871,304, 4,872,820, and 5,082,222, for example, disclose fluid compressors of a type in which the refrigerant gas of the refrigerating cycle is compressed while conveying the gas in the axial direction of the cylinder.
There is also another type of fluid compressor as shown in FIG. 7. In a general compressor, refrigerant gas is taken into the device from a main bearing 1 side, and compressed toward a sub-bearing 2 side. However, in a fluid compressor of this type, a thrust force works on a rotation rod 3 due to pressure difference of the refrigerant gas. In order to balance the thrust force, a pressure introduction hole 4 is formed in the rotation rod 3. Refrigerant gas at a suction pressure is introduced into an internal cavity 5 of the sub-bearing 2, and an end face of a sub-axis 6 of the rotation rod 3 is pressurized. The diameters of the sections of the rotation rod 3 are determined such as to cancel out thrust forces for balance.
The diameter of the main body of the rotation rod 3 is set to be larger than that of a main shaft 9. The main shaft 9 is inserted into an internal cavity 10 of the main bearing 1. A part of the end surface 11 of the main body 8 and a part of the end face 12 of the main bearing 1 face closely with each other. A suction hole 13 is formed in the main bearing 1, and serves to connect a suction tube 15 associated with a sealed case 14, and an inner space of a cylinder 16 with each other. The refrigerant gas passes through the suction hole 13, and is introduced to the operation chamber formed in the cylinder 16.
FIG. 7 also depicts a discharge tube 17, which is connected to the sealed case 14 to be associated with the inner space thereof.
In a fluid compressor of the above-described type, a refrigerant gas is used to balance thrust forces. Consequently, the diameter of each of the main shaft 9 and the sub-shaft 6 of the piston must be determined such as to have a sufficiently large cross section area. However, as the diameter of the main shaft 9 increases, the thickness of the main bearing 1 decreases.
In order for the cylinder 16 to take a sufficient amount of the refrigerant gas therein, the suction hole 13 should have a large passage area. However, if the diameter of the suction hole 13 is simply set large, the opening of the suction hole 13 is partially covered by the end face 11 of the main body 8, and therefore the amount of the gas taken in the cylinder does not increase.
In consideration of the above, in order to have a sufficiently larger passage area, there should be provided a plurality of suction holes 13 as shown in FIG. 8A, or the suction hole 13 should be made into a deformed elliptic shape as in FIG. 8B, thereby increasing the production cost of the main bearing.
Further, the pressure introduction hole 4 and the suction hole 13 must be separately provided, and the pressure introduction hole 4 is the main factor of increasing the production cost.